1. Field of the Invention
This invention generally relates to electrical terminals for mounting electrical components on printed circuit (PC) boards and, in particular, to a terminal having a frangible mounting leg suitable for mounting through a mounting hole on a PC board without cutting, deforming or otherwise damaging or effecting the integrity of the PC board.
2. Description of the Prior Art
The conventional way to mount small electrical terminals (like pins and single leg tabs) on a PC board is to force the mounting legs of the terminals into holes on the PC board. The hole diameter is generally smaller than the diagonal or diameter of the mounting leg, so that there is an interference or press fit as shown in FIG. 1. FIG. 2 is an enlarged cross-section of the mounted pin of FIG. 1, showing the interference fit after soldering.
Where a press fit created between the terminal leg and the PC board hole is tight, it produces stresses in the PC board which, if excessive, can crack or warp the board. Also, with a press fit the insertion force may be significant, and this may deform the terminal. An interference fit also frequently produces board material shavings and excessive board material displacement around the hole which make soldering more difficult and can produce a weak solder joint.
A solid single leg terminal is disclosed in U.S. application Ser. No. 07/415,965 filed Oct. 2, 1989, assigned to the assignee of the present application, which is incorporated herein by reference. The aforementioned application discloses a number of prior art approaches which, however, have not proven satisfactory, and an improved design was proposed to overcome the disadvantages of the earlier designs.
However, since the proposed mounting leg has dimensions generally smaller than those of the mounting hole, the mounting leg is received loosely therein and does not always provide lateral or sideway support during the splaying process. It has been found that in some cases splaying does not follow the coin along the center of the leg, but favors one side and results in an asymmetrical one sided splay. Such off center splaying has a tendency to further pull the terminal pin off the original center line perpendicular to the PCB surface. It has also been found that such off center splaying occurs even if the coin is absolutely in the center of the leg. In such cases the splaying tool leaves the coined groove and starts to cut into the side of the leg even if the coin is very deep. Further, such asymmetrical splaying is self fueling. Any propagation in one direction and resulting imbalance of forces on the anvil cause it to move in a direction which accelerates the imbalance. Eventually, in the worst case, the splay runs out of one side of the leg completely shearing it off.